Download Thermometers and Thermocouples

Thermometers and
Thermocouples
Physics Project
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Thermometers
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Thermometers
• A thermometer is a device that measures
temperature changes, using a variety of
principles and a range of set values.
• Thermometers measure temperature in
Fahrenheit, Celsius or Kelvin.
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Digital Thermometers
• These thermometers have a thermistor which acts
as a temperature sensitive electric resistor.
* A thermistor is a device made of materials
which are thermally sensitive.
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Simple Thermometers
• These thermometers are calibrated to the melting
point of ice (0 °C) and the boiling point of water
(100 °C). They usually contain Mercury or
Alcohol in the bulb to detect temperature change.
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Sensitivity
• Sensitivity of a thermometer refers to its
ability to give a large response to a small
change in temperature.
• Sensitivity can be increased by making a
large bulb and a narrow glass tube so that
even the smallest change in the liquid level
is noticed easily.
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Range
• The range of temperatures measured by
different types of thermometers vary greatly.
• For example a mercury-in-glass
thermometer can measure temperatures below
-38° C up to 357 °C where as an alcohol-inglass thermometers can record temperatures
from -114 °C to 64.7 °C .
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Accuracy
• An accurate thermometer is one
that gives correct values of
temperature.
• Note: Accuracy should not be
confused with sensitivity as a
sensitive thermometer is not
necessarily accurate.
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Usage of Hg and Alcohol
• Thermometers contain mercury/alcohol because :
i) They are denser than water
ii) They have high freezing and boiling points.
iii) They do not stick to their container.
iv) Mercury is sensitive to even the
smallest
changes in heat level.
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Thermocouples
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Thermocouples
• A thermocouple is a device which has two junctions
between two different metals which are connected to a
voltmeter.
• One junction which is kept at room temperature is
known as the cold junction and the other junction which
is kept at the point where the temperature has to be
measured. It is called the hot junction.
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• If the temperature at both the junctions is
same, there will be no current as both the
voltages will cancel each other out.
• If there is a change in the temperature, the
metals join (touch/come in contact) with
each other and produce a voltage.
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Advantages
• Thermocouples can measure very high
temperatures. Up to 2600°C.
• It is accurate.
• Is very sensitive and so displays the
temperature change rapidly with minimum
delays.
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Disadvantages
• It has a complex operational method
and can not be used by the general
public.
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Made by: Sana Munawar
Damaisha Naseem
Grade 10-B
hope you like our project =)
visit www.physicsatweb.com and enjoy a lot of stuff with phys uncle